Micro-cracks in aircraft primary structures or nuclear plants can easily spread over long periods of time and, if undetected, may lead to catastrophic failure conditions. Non-destructive evaluation (NDE) techniques are a necessary tool to guarantee that a component is free of any harmful damage. Thermosonics (also known as ultrasonic stimulated thermography) is an NDE technique that uses an infrared camera to image material defects by detecting the frictional heating at crack surfaces when a part under inspection is vibrated. These vibrations are produced by a high-power ultrasonic horn being pressed against the surface of the component under investigation. Thermosonics has the advantages of being rapid, affordable and more sensitive to micro-cracks detection than traditional infrared thermography. However, the ultrasonic horn used in thermosonics is a crude means of exciting vibrations. The mechanical contact between the material and the horn typically results in an uncontrolled generation of vibrations, which makes thermosonics results non-reproducible and, therefore, this technique not reliable. NUSIT proposes a reliable and reproducible alternative to thermosonics by developing a novel hybrid NDE inspection method, here named as nonlinear vibro-thermography, obtained by a combination of nonlinear ultrasonic techniques and thermography. Nonlinear ultrasonic methods measure the material nonlinear effects caused by the interaction of ultrasonic waves with the "clapping" motion or the frictional contact between micro-crack surfaces. As a result of this interaction, other frequency components of the single input frequency can be generated. These new frequencies indicate that a damage is present within the material. Nonlinear ultrasonic methods will provide in NUSIT a reliable means to select the input frequency that will enhance these material nonlinear effects. This will allow high sensitivity to micro-cracks detection and repeatability. Traditional thermography will be then used to image the frictional heating at the damage location. The input frequency selection process will also be optimised in NUSIT by analysing the concept of nonlinear local defect resonance for input power reduction. This eighteen-month project will be mainly focused on assessing real-life material damage such as corrosion micro-cracks in metallic structures and impact flaws in composite materials. To accomplish these objectives, NUSIT is supported by the Nuclear National Laboratory and Rolls-Royce that are providing a set of steel nuclear storage canisters with corrosion micro-cracks and impact damaged composite aero-engine components as in-kind contribution. Nonlinear vibro-thermography will produce a step-change in the non-destructive inspection of both metallic and composite materials by ensuring rapid and affordable inspection of large areas and complex geometries, reliable excitation and high sensitivity to the presence of micro-structural flaws. The overall aim of NUSIT will be to take nonlinear vibro-thermography out of the laboratory and introduce it successfully into industry.
|Effective start/end date||1/05/16 → 31/10/17|
- Engineering and Physical Sciences Research Council